Stability of a power system includes synchronization stability, voltage stability, and frequency stability. The synchronization stability is derived from the fact that a main power generator of the power system is a synchronizing power generator. The synchronizing power generator has a phase angle of a rotor which differs depending on an interconnection position on the power system, but basically operates synchronously at the same rotation speed. However, if disturbance such as a system failure, for example, a ground fault or the like, or a sudden change of an output of a distribution power source occurs, the phase angle of the synchronizing power generator fluctuates. If the phase angle fluctuation expands and propagates, the synchronizing power generator cannot be synchronized with the rotation speed, thereby, leading to step-out.
In order to attenuate the phase angle fluctuations, a stabilizing device is installed in the power system. Specifically, by changing an excitation voltage of a power generator, changing an output of active power or reactive power of a power storage device, or changing impedance of a variable impedance type series capacitor, the phase angle fluctuation is attenuated, and thereby, the stability of the power system can be improved.
A control device for controlling the stabilizing device detects a signal which varies in accordance with the phase angle fluctuation, for example, a line power flow or a frequency deviation, and outputs a control signal by increasing a gain or compensating a phase for the signal. A stabilizing effect according to a control parameter such as a magnitude of the gain or a time constant of phase compensation differs depending on a device state of the stabilizing device which is a control target or a power flow state of the power system.
For this reason, a method for determining the control parameters of the stabilizing device is reviewed, and there is a technology described in, for example, PTL 1. PTL 1 discloses that “a configuration is provided such that a ratio of addition of the amount of control operation which is an output of a plurality of control means is changed on the basis of a magnitude of fluctuation detected from an input signal of operation amount control means, and thus, effects are obtained in which a circuit capable of determining a ratio of the amount of control operation can be realized without requiring a complicated circuit, a ratio of cooperation according to a magnitude of fluctuation can be easily controlled, and thereby, fluctuation in a wide frequency range can be reduced and stability of a power generator can be improved”.